Electron discharge device



Original Filed July 2, 1928 Patentes Feb. is, 1937 t 2,070,691

UNITED ysTATEs PATENT OFFICE ELECTRON DISCHARGE vDEVICE Percy L. Spencer, Medford, Mass., assigner, by mesne assignments, to Raytheon Manufacturing Company, Newton, Mass., a corporation of f Delaware Application .my 2, 192s, serial No. 2821845 Renewed March 5, 1934 8 Claims. (Cl. 250 -'27.5)

My invention relates to an electron discharge kaline-earths so that they cohereA firmly in the device and has particular application to rectiers desired form, and adhere more firmly thereby of the gaseous type. Recti'ers in which spaced increasing the life of the material.

electrodes operate in a rareedatmosphere are. In general the tube embodying my invention old and have been used for the rectication of comprises an exhausted envelope having a rare- 5 currents of low value at moderate voltages. fied atmosphere of one or more of the rare gases Such rectiiiers whether thermionic or cold cathand which may have in addition one or more alode type, are characterized by a simplicity of kali or alkaline earth metallic vapors to reduce mechanism as wellasoperation,which make them the potential drop. Within this envelope and l very desirable for energizing vacuum tubes from operating in such an atmosphere are cooperating 10 lighting current. However, such rectiers have electrodes comprising a cathode and at least one hitherto been under the great disability of not and preferably two anodes symmetrically disposed being able to carry much current compared to with respect to said cathode. 'I'he cathode which the demands which a, multi-tube modern radio may be of any refractory material has its surface l receiving Set requiree 1t is very undesirable beso treated that it possesses a low Work function. l5 cause of expense to greatly increase the size of Conversely theractive surfaces of the anode may, such reetiers so thetal greater output may be if desired, be so treated that they have a correhad. For the same reason, the duplication of two sDOndingly high WOrk function, which has a or more tubes is undesirable, especially since such tendency 0f inhibiting reVeIse discharge.

tubes because of their characteristics are coupled In the Case 0f non'thel'mienie Cathode, it is s0 20 in tandem only with the aid of auxiuary devices. fabricated that it has very large surface area The result is that i-eetiei` tubes of this type as compared to its mass and is preferably formed of generally used in battery eliminators for radio a metallic Wafel- In Order t0 render this type 0f sets, have a maximum output of about 1/8 amp, Cathode more eiicient, both in starting and oper- In order te render a muititube set Completely ation, it is preferably, though not necessarily, so 25 a. c. operated, it is highly desirable that the eveilshaped that there is a considerable concave active able rectified output be of greater value. Surfaee- One object of my invention, therefore, is to de- The hen-theilnloni type is Preferably providvise a, reotier 0f the ygaseous Conduction type ed with concave active surfaces. The discharge which is substantially of the same physical size from a Cethede generally tends t0 Concentrate 30 as ordinary rectifiers, but which at the same time, along Such Surfaces probably because POsitiVely will have a much greater current carrying capac charged ions appear to have a tendency to conity. Another object is to devise such a rectifier gregate lh a space Which ls partially 0r COmpletewhich Win be simple, easily manufactured, and of ly surrounded by active cathode surfaces. In thus substantially the same cost as prior rectifying cengregatihg, they tend t0 attract more eleC- 35 tubes of this type. Further 'Objects are to devise trons from the cathode surface, thereby creating a rectifying tube which will give a high current a Very 10W dIOD in said slllfee- BY shaping this output at a high eficiency coupled with a long type of cathode so that there is considerable aciife and which win have no e1ements1iab1e to be tive Surface having a concave curvature. the tendburned out. ency of the cathode discharge to concentrate in 40 My invention also relates to cathodes for eleca pocket is promoted, thus rendering the starttron discharge apparatus and applies equally well ing of the tube easier and its operation certain to the thermionic and non-thermionic type. An and steady. The mass of the cathode is preferobject of my invention, therefore, is to devise a, ably small for reasons to be explained hereafter. cathode which has a low Work function and can, Although a discharge in the non-thermionic 4U therefore, emit electrons copously. A further obtype 0f reetier Will be easily initiated and eiject is to obtain such emission from a thermlonic ciently maintained With just the eleetredes as cathode without heating the cathode to an excesmentioned, it is preferable, though not essential, 5e sively high temperature. Another object is to to surround the region of discharge with an en- Ohtain Such emission fi'Om ,a tneTiniOniC eathOde closure of metallic members. This enclosure without introducing excessive losses at the cathtends to conserve the heat produced by the disode surface. Another object of my invention is charge, thus rendering it possible to maintain the production of electron-emitting material conthe discharge with greater eiciency. Further- 55 sisting of metallic material impregnated with almore, by completely enclosing the region of dis- 55 tial.

2 charge, the discharge is maintained between the desired active sur aces and is prevented from causing damage to the insulating or containing structure.

The shielding member is preferably insulated from the electrodes, and the insulation is preferably, though not necessarily, effected by the provision of short path insulating BDS.

In operation, the non-thermionic type of tube is characterized by the initiation of a glow discharge upon the application of a suitable poten- This glow discharge is visibly manifested by diffused glow encompassing the entire cathode. Almost immediately a small ball of ilre appears to settlevon the surface of the cathode, moving very swiftly therealong and is nally located in a pocket of said cathode. time a brilliant glow surrounding the cathode shrinks in size but gains in brilliancy and becomes mergedwith the ball of fire. Each of the anodes has a bright region partially or completely surrounding it. This region is .not as intense as the ball of nre and is not as large. 'I'his optical change in the character of the discharge is the physical manifestation of a change from the character of a glow discharge to that of an arc-like discharge. This change in the character of the discharge is accompaniedl by a drop in potential across the tube and an increase in the current through it.

Though I am not certain, it is my theory that this discharge is extinguished every cycle during the reverse period but is re-established by means of a hot spot on said cathode. This hot spot is suilicient to initiate the arc by means of thermionic emission. By making the cathode of small mass, the hot spot is effectively maintained during reverse periods. However, it is very unlikely that the' operation of the cathode may be characterized as thermlonic, even in a. substantial degree, since the amount of current in the arc is far greater than thermionic emission from the active area of the cathode would warrant.

substantially the same as the ordinary gaseous type of rectifier, can very easily rectify a current of V3 amp. and has actually passed more than 1/2 amp. throughout steadily and without any serious injury apparent. The voltage at which such current may be rectified may be substantially as high as the prior art rectiilers of this general type or may even be somewhat greater. voltages as high as 600 across the anodes at the currents mentioned above, have been successfully rectified. In one case, such rectiers gave a combined output of 1100 volts at 1/2 amp. The cathode in such tubes is composed of a piece of tantalum 1/2 inch square and .003 inch thick.

In case of the thermionic type of rectifier, the cathode emitted electrons copiously at a. reddish white heat.

Referring to the tially full size,

Figure 1 shows a sectional view of a rectifier embodying a preferred form of my invention;

Figure 2 is a plan view of the anodes;

Figure 3 is a detailed sectional view of the anode insulating structure;

Figure 4 shows a modified form of cathode.

Referring to the drawing, I is the ordinary glass or other insulating envelope within which is a press 1. Supported on press l are two anodes 4 having drawing, which is substan- -gas particles in said rectifier.

A tube of this character and of asize..

a bridge of four of I cathode 4and lead-in wires II and I3 sealed in said press. A cathode 8 is suitably supported on a wire-like member in the press to a lead-in wire I2. Wires II, I2, and Il from the anodes and cathode are joined to pins Il, Il, and I6 of base I1 which is suitably cemented to the bottom of envelope of I. 'I'he tube is adapted to be plugged into a socket so that pins Il, I5, and I8 are connected to the secondary of a transformer are connected to the extreme ends of the secondis connected through a said secondary.

insulators 8 of ary while the cathode load I8 to the center of The anodes are surrounded by lava or any suitable material tting into pro- :lections 6 of press 1. As may be seen, these insulators have suitable shouldersso that the insulators will be supported by the projection 8.

- Each of said insulators has a center channel through which the Ianode and the lead wire pass.

,At the outer portion of said insulator 5 are fitted metallic bushings 8 of steel, aluminum, nickel, or any other suitable material. 'Ihe bushings and insulator ends have conjugate interiitting surfaces so that the bushings may be fitted down and rest upon the insulators. Each of said bushings 8 has its center portion cut out to form a channel coaxialwith said anodes and somewhat larger so as to leave region, though of considerable depth compared to the space between the anode surface and the inner bushing surface, is of such dimension that vthe distance between opposing surfaces is preferably of the order of the mean free path of the In this way, bombardment by ions and electrons of the insulation is effectively eliminated. It is, of course, possible to dispense with bushings 8 entirely and suitably shape insulators 5 so that there is a region similar to that shown. Cathode supporting member 9 passes through an insulator I0 composed of lava or similar material retained in place against a plate 28 by means of a'n annular metallic member 50 `which clamps the insulator in place. This member 50 is put over insulator I0 and thereafter welded to plate 20. It will be noted that the insulator and plate are cut away in the region of wire 9 to form a gap somewhat similar in form and function to the gaps around anodes 4.

Plate 20 previously mentioned above. is suitably apertured as shown in Figure 2 so that bushings 8 flt in. The upper free ends of bushings 8 are suitably shouldered so that plate 20 may be tted thereon and supported thereby. The entire assembly of insulators and bushings with plate 20 is such that the electrodes are iirmly retained in their relative position. Although plate 20 may have any configuration desired, it is preferable to have it circular. Covering the electrodes and active region of discharge from the top and sides is a dome-like member 2l which is, welded to 20 at their meeting edges. Sealed in press 1 are two supporting wires 5I and 52, which, although not shown in the drawing, are welded to opposite points of the meeting edges of 20 and 2| to support the entire structure.

Cathode 3 which is welded to or suitably supported by member 8, is composed of a thin rectangularly shaped wafer of small mass.l This wafer may be nat or substantially flat as dis--` closed in my prior application, Serial No. 183,405, filed April 13, 1927,of which this is a continuation in part. But preferably this wafer is curved over on itself to form a U-shaped member. Each of the four corners is thereafter flared out as more I8. The two anodes an annular region. 'I'his` 8. This member is sealed clearly shown in Figures 1 and 2. While the cathode may be yof any refractory material suitable for use, such as tantalum, platinum, or tungsten, I prefer tantalum. In order to impart to the surface of the tantalum or other cathode material a low work function, I coat the surface with certain substances. In the case of tantalum, I preferably oxidize the surface ilrst in any suitable manner as by heating in gas name. Thereafter mixture of solutions of nitrates of barium, strontium, potassium, and if desired, other alkaline earth or alkali metals. These dissolved nitrates are burned into the metal by an intense ame. 'Ihe process is thereafter repeated as often as may be desired. In the case of tantalum, the surface of the metal crusted. and rough, while the metal itself becomes brittle. 'I'he latter indicates that lthe inner layers of metals have been reached and transformed by the alkaline earth and alkali metals. 'Ihis operation is performed several times. While I am not certain as to exactly what happens, it is my belief that the nitrates become transformed by obscure chemical reactions into oxides. These oxides coating the outer surface of the metal impart thereto a low -work function of desirable character.

In the case of a thermionic cathode, especially of the lamentary type, the same procedure is followed except that the metal is in Wire form.

'Ihe anpdes may be of any suitable material such as iron, nickel, aluminum, tungsten, talum. To impart a high work function to the surface of the anodes, itis desirable to transform the metallic surfaces into oxides. 'I'his may be heating in a ame or heating to white heat during the welding of the anode and its lead-in wires. By thus treating the anodes, the

tendency of reverse discharge to the cathode or arcing between anodes is effectively eliminated. the anodes would be made The gas or gases are preferably, though not necessarily, of the inert group and may comprise helium alone or a mixture of helium and argon or neon or any two of the above. If desired, a vapor of an alkali or alkaline earth metal such as caesium or potassium, may be admitted to reduce the potential drop between electrodes.

In Figure 4, I have shown a modified form of non-thermionic cathode in which a cylinder is used. This cylinder, .although shown with its axis perpendicular to the line joining the two anodes, may be disposed in any manner whatsoever, both as regards its horizontal inclination to the line joining the anodes and the vertical inclination to the plane of plate 20. If desired, this cylinder may be vertical ormay very well be in such position as to enclose the line joining the two anodes.

I claim:

1. A rectifier comprising a plurality of anodes and a cathode in a rareied atmosphere, means comprising a metallic member completely enclosing the region of discharge, said metallic member being electrically insulated from said electrodes by mean free path spacing, said cathode being I spray the cathode with a appears to become white, ena 3 made of tantalum with alkaline earth metal compounds burned in so that the discharge starts as a glow and continues thereafter as an arc-like discharge.

2. A non-thermionic cathode of tantalum in the form of a doubled over wafer having alkalineearth metal compounds burned into its surface.

3. A gaseous discharge rectifier of the type wherein the discharge is initiated in the form of a glow, comprising a gas tight envelope containing a relatively large-area cathode, a relatively small-area anode, and a gas lling at a pressure sufficiently low to prevent flow of substantial glow current from said anode to said cathode under application to said anode of a negative potential higher than the breakdown voltage of adjoining surfaces into intensified discharges, and extension surfaces diverging from said cavity portion and having sufllcient area and angularity to cause glow discharges emanating on said adjoining extension surfaces to converge into said cavity portion and produce an arc-like discharge between the cavity portion and said anode at a fraction of the cathode fall voltage of the gas, the interior sides of said cathode cavity portion being made of tantalum with low-work-function metal compounds burned into the tantalum surface. f

4. A gaseous discharge rectifier of the type wherein the discharge is initiated in the form of a glow, comprising a gas tight envelope containing a relatively large-area cathode formed of a conducting member having a cavity portion with closely folded walls and a portion with extensions aring outwardly from theclosely folded Walls, a relatively small-area anode, and a gas filling at a pressure sufficiently low to prevent flow of substantial glow current from said anode to said cathode under application to said anode of the adjoining cathode extensions being sulciently large to cause glow currents developed over the area of said cathode to converge into an arc-like discharge emanating from the space between the closely spaced cavity walls and operating at a fraction of the cathode fall voltage, the interior sides of said cathode cavity portion being made of tantalum with alkaline-earth metal compounds burned into the tantalum surface.

5. The method of making an electron-emitting cathode which comprises oxidizing a metal surface, coating said metal surface with an alkaline earth metal compound, burning said compound into said surface, mounting said cathode within a vessel, and exhausting said vessel while heating said cathode to a high temperature.

6. The method of making an electron-emitting cathode which comprises coating a metal surface with a material having a low work function. burning said material into said surface by an intense flame, mounting said cathode Within a vessel, and exhausting said vessel while heating said cathode to a high temperature.

7. A gaseous discharge rectifier comprising a gas-tight envelope containing a relatively largearea cathode formed of a conducting member having a cavity portion with closely folded Walls and a portion with an extension daring outwardly from the closely folded walls, an anode and a having a low work function coating tenaciously gas tllling, the width of the cathode cavity being retained on its surface. sumclently small and the area of the adjoining 8. A rectier comprising an anode and a cathcathode extension being suillciently large to cause ode in a rarefled atmosphere, means comprising 5 yglow currents developed over the area of said a metallic member enclosing the region of dis- 5 cathode to converge into. an arc-likel discharge charge, said metallic member being electrically emanating from the kspace between the closely insulated from said electrodes. said cathode being spaced cavity walls and operating at a fraction made of tantalum with alkalineearth metal comof the cathode fall voltage, the interior of the pounds burned in.

1o sides or said cavity portion being made of a metal PERCY L. SPENCER. 1o 

